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Manganese phosphate removal from steel. What chemicals will do this?

Q. I have an occasional need to strip manganese phosphate coatings from finished steel parts for dimensional inspection. I need a chemical solution that will remove the coating without attacking the base metal. Any help would be appreciated, Thank you, John

John D'Annunzio.
technician - Bohemia, New York
January 20, 2010

A. This is done all the time by those firms doing manganese phosphate and having to determine coating weight. Coated steel coupons of known are weighed, the coating stripped in hot chromic acid solution and then reweighing the stripped, bare and unetched steel coupon. The whole basis of this method of determining the coating weight is that the strip doesn't touch the steel - only the phosphate is dissolved. Check out the DOD-P-16232 [ed. note: replaced by MIL-DTL-16232 [from DLA] ] or any manganese phosphate spec for the details.

Milt Stevenson, Jr.
Syracuse, New York

"hot chromic acid solution"

Would this process also remove Zinc Phosphate? I was given a gun barrel that needs the coating removed because it was also coated on the inside of the barrel. I think its Zinc because its lighter in color than manganese.

Thanks for your time,

Mitch Shepard
- MPLS, Minnesota

Q. How to remove manganese phosphate coating on steel to measure the coating mass?

Shashi Kumar
consultant - Bangalore, Karnataka, India
January 27, 2014

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